Video may be in progressive or interlaced form. In progressive video, all of the lines of a video frame are drawn in sequence. Interlaced video, on the other hand, comprises a sequence of fields, where each field contains either the even or odd lines of a frame. The fields alternate between the even and odd lines of a frame, so, over time, scan lines throughout the frame are displayed in space, even though a given field does not contain all of the lines together at any point in time. Because of the physics of the Cathode Ray Tube (CRT) display technology, a CRT monitor or television set can display interlaced video natively without any apparent artifacts. Other display technologies, such as Liquid Crystal Display (LCD) and plasma, use some form of deinterlacing to produce progressive video by filling in the missing lines in each field when that field is displayed.
Deinterlacing is typically performed by interpolating a pixel that is missing in a frame from other pixels that are present nearby in either space or time. A pixel's value may be interpolated based on pixels that appear vertically above and/or below that pixel in the same field (spatial interpolation), or based on pixels that appear in the same spatial position in the previous and/or subsequent fields (temporal interpolation). For example, in order to interpolate the value of a pixel, the values of the surrounding pixels (either in space or time) could be averaged. (Averaging could be performed on values of any type of pixel representation, such as grayscale, RGB values, YUV values, etc.).
Some deinterlacing techniques choose how to interpolate a missing pixel based on whether the pixel appears to be moving or not. If the pixel is moving, such techniques typically interpolate the pixel spatially; otherwise, they interpolate the pixel temporally. These techniques may produce various kinds of visual flaws.